Re-enable pre-commit tests

Author: felddy

.travis.yml

@@ -23,6 +23,8 @@ cache:
   pip: true
   directories:
     - "$HOME/.cache/pre-commit"
+install:
+  - pip install --upgrade -r requirements-test.txt
 script:
   - pre-commit run --all-files
   - travis_scripts/build_docker_image.sh

requirements-test.txt

@@ -0,0 +1 @@
+pre-commit